Ash feed control



Oct. 11, 1960 E. B. ToLMAN ASH FEED CONTROL Filed April 1s. 1958 atet gel 2,955,379

Patented Oct. 11, 1960 ASH FEED CONTROL Edgar B. Tolman, Winnetka, DI.,assigner to United Conveyor Corporation, a corporation of Iliinois FilesApr. 16, 195s, ser. No. 728,990

9 claims. (ci. 3oz-s2) This invention relates to apparatus for feedingash from a furnace to a storage bin, and in particular it relates tomechanism for controlling the rate of flow of ash into a vacuum or otherpneumatic conveyor system.

Ash from high efficiency coal furnaces of the type used in electricpower generating plants is exremely tine, and presents special problemsin handling and disposition. A modern electric generating plant producesseveral tons of ash per hour, and this is conveniently handled in vacuumconveyor systems. Because the ash is eX- trernely tine, it is quitediflcult to handle due to arching, slumping of large masses of ash intothe conveyor conduit, and other phenomena which produce uneven flowthrough the vacuum system and into a storage bin.

The ash handling system for a high capacity electrtic power plantcommonly has severalA hoppers which receive ash from each furnace, andthese hoppers act as temporary receptacles from which the ash is fedinto the vacuum conveyor conduit for transmission to the storage bin.Conveniently, the system is arranged to handle ash from one boiler, orfurnace, until all of the hoppers serving that furnace are exhausted;after which the system is switched so that ash is fed from the hoppersserving another furnace. The present system provides relatively evenflow of ash from all of the hoppers serving a single furnace so as tominimize clogging ofthe vacuum conveyor conduit, and also permits allthe associated hoppers to remain in communication with the vacuumconduit even though one hopper may empty sooner than another. This, ofcourse, simplies the control mechanism by making it unnecessary to closeo the discharge opening of an empty hopper while the associated hoppersare still discharging. A group of associated hoppers may be put intoVthe ash discharging cycle at the same time, and the control mechanismneed not provide for segregating one or more hoppers of the group whilethe others are feeding. Feed of ash from the entire group of hoppers isterminated at one time, and the system may then be switched to anothergroup of hoppers serving another furnace.

The operation of a vacuum conveyor system requires that the rate of flowof ash into the vacuum conduit remain fairly uniform. A certain negativepressure is required in the vacuum conduit merely to overcome theinternal resistance of the system. The vacuum, of course, must beincreased to overcome the added resistance to ow which results fromintroducing ash into the conduit. Accordingly, a system which has an airexhauster adapted to produce a particular negative pressure in thesystem will clog if a large quantity of ash suddenly enters the conduit.As long as the ash load remains constant at the optimum for theparticular conveyor system, the vacuum remains constant. -If excessmaterial enters the conduit, the iiow of air through the system isinhibited, and this increases the negative pressure in the conduitbetween the air exhauster and the excess load of ash. Conversely, if thevolume of ash entering the conveyor conduit is reduced, the vacuum aheadof the air exhauster becomes less. This fact is utilized in the presentsystem to control the feed of ash into Vthe conduit by means of suitablevacuum controlled valves.

Each hopper in the present system is provided with an ash feed-opening,and associated with the ash feed opening is a conventional mechanism forfluidizing the ash so that it flows readily through the opening. Thefeed of ash is not controlled by opening and closing the feed openings,but instead is controlled by starting and stoppin-g the flow ofiiuidizing air to the fluidizing units associated with the feedopenings. The Vacuum controlled valves admit fluidzing air until suchtime as au increase in the vacuum of the system results from excessiveash in the conduit; and this increase in vacuum is utilized to suspendthe aerating air until the vacuum in the system again decreases to thepoint where the system can handle additional ash, at which point the owof aerating air is resumed.

The present disclosure deals only with pressures which are belowatmospheric, so in the specification and claims the word minimum is usedto refer to a pressure nearest to atmospheric, while maximum refers to apressure farther from atmospheric. p Intermediate refers to a pressure-between maximum and minimum, reduction of vacuum means that the vacuumsystem approaches atmospheric pressure.

The invention is illustrated diagrammatically in the accompanyingdrawing, which illustrates the control for two hoppers which feed intothe vacuum conduit simultaneously. When. thetwo illustrated hoppers areempty, they are segregated from the conduit and a similar group ofhoppers (not illustrated) is placed in communication with the conduitunder a similar control system.

Referring to the drawing in greater detail, the system includeshoppers,-indicated generally at 1 and Z, which are providedrespectively, with outfeed mechanisms, indicated generally at 3 and 4.Each hopper is the bottom portion of a centrifugal or electrostaticseparator of conventional design, which separates ash from the hot aircoming out of a furnace. Outfeed mechanisms 3 and 4 have discharge pipes5 and 6, respectively, which are connected to a vacuum` conduit 7; andthe conduit 7 feeds through a conventional centrifugal separator S wherethe ash is removed from the conveying air stream for deposit in astorage bin 9. From the separator 8, the air passes through a suctionconduit 16; and air iiow through the system is provided by conventionalfluid operated air exhauster, indicated generally at 1i.

The flow of ash into the conduit 7 from the feed mechanisms `3 and L- iscontrolled by a vacuum system indicated generally at 12, which includesa vacuum control pipe i3 connected to the vacuum conduit 1?.

The two ash hoppers and their associated ash feed mechanisms areidentical, so only the hopper l and the feed mechanisms, 3 are describedin detail. Each hopper has a continuous upright side wall 14 which isthe lower part of a separator, and which merges into a frustopyramidalbottom f5 provided with a discharge throat 16 through which ash entersthe feed mechanism 3. in the bottom portion 1S of the hopper is anarrangement of fluidizing stones i7 which are spaced apart to aiford apassage 18 through which ash flows to the throat i6. The hopperconstruction here disclosed is disclosed and claimed in my copendingapplication, S.N. 728,989, filed April 16, 1958.

The ash feed mechanism 3 consists of VaV chamber 19 having an inclinedfluidizing stone 2l), and a feed opening 21 in one Vwall of the chamber19 has its lower margin ush with the surface of the uidizing stone 20 sothat uidized ash in the chamber 19 may ow through the pipe reached,valve 29 again opens.

obvious to those skilled in the Y Vfor the uidizing stones 17 inithehopper 1-,7' a branch line 26 forV theiluidizing stone 20 in ythe feedmechanism 3, and similarbranch lines 27 and 28 for the correspondingparts Yof the hopper 2 and feed mechanism 4. Y

Flow of iluidizing air toV the branch lines to 28, 'inelusive, iscontrolled by a solenoid valve 29, which in turn is opened and closedbya vacuum switch inthe vacuum control Vpipe 13. When the system isfirst started,

The feed mechanism 3 also Y 2,955,879 Y. c 'Y feed opening ofsufficiently small area in proportion to the area of all of saidopenings thatthe reduction of vacuum thereV must Vbe a vacuum Within theconduit 7 before any ash is fed out of the hoppers. Accordingly, y Y vthe vacuum switch 30 is set to open the solenoid Vvalve 29 at apredetermined minimum pressure which is suitable for the Vparticularinstallation. This admits low pressure air 'from the supply line 24 tothe uidi'zing stones 17 and Zt? and so lluidizes, Vor aerates, the ashin the lower portions fof the hoppers Vand the associated feedmechanisms that the ash may ilow freely through the feed openings 21into theconduit 7. As the ash load'in conduit 7 increases, the pressurein the vacuuml control pipe 13 approaches the maximum which can beproperly utilized with the particular air exhausterY 11 in the system.VIn

' a typical system the maximum negative pressure might be 18 inches Hg,or greater in certain types of systems.

in said conduit resulting from'the free flow of air through a hopperproduces only aY small reduction in the ashmoving characteristics of theapparatus; aerating means for simultaneously aeratingV the ash in allsaid chambers; a solenoid valve for controlling said air supply; and avacuum controlled electric switch in said vacuumV systemV for operatingYsaid valve in accordance with predetermined pressures in saidsystem,wwhereby the aerating means operates to facilitate flow of ashfrom thehoppers'to the conveyor system when the pressure in said systemis within a predetermined range.

2. Apparatus for feeding ash at aeontrolled rate; comprising: aplurality of ashV receiving hoppers; a vacuum conveyor conduit; anoutfeed mechanismV for each hopper, eachsaid mechanism including anYaerating chamber having a constantly open feed opening through whichash passes from the hopper to said conduit, the area of each openingbeing sufficiently small in proportion to the total area of all saidopenings that the reduction of vacuum in said conduit resulting fromfreeflow of air through a hopperproduces only a small reduction in theash moving characteristics of the apparatus;` means for aerating ash ineach of said chambers to facilitate theow of ash from said hoppers tosaid conduit; and means controlled by the amount of ash in saidconduitfor selectively actuating said aerating means.

If the ratevofilow of ash into the conduit 7 is heavy Y enough to bringthe negative pressure in the vacuum control pipe 13 above the optimum of18 inches Hg, the pressure acts upon the vacuum switch'30 lto close thesolenoid valve 29 and'thus suspend the ow of aerating air to the stones17 and 20.1-A Flow of ash into conduit 7 is thereby `suspended and thepressure -in the control pine 13l approaches an intermediate pressureat'which efficient operation of the system Yrequires that the ow of ashbe resumed. ,When the intermediate pressure is The pressure differencebetween the suspension of flow and resumption of flow may be 3 or 4inchesHg. Thus uidizer 20 constitutes ow control means positionedbetween hopper 1 and conduit 7 to control the movement of ash from thehopper to the conduit and varies rapidly between a first condition whichpermits no movementof ash into therconduit and a second condition Ywhichpermits maximum movement of ash into the conduit'.

A great advantage of the present system is'that it permits the use offeed openings 21 from the feed mechanisms which are lsmall enough thatthe valve 22 need not still feeding.V The ash owis controlled entirelyby fluidi izing it, andthe valves 22 are closed only when allthe hoppersof a group are emptied.' The system is illus- Y trated with only 2hoppers in a group, but a typical large ness of understanding only andno unnecessary limitations should be understood therefrom, asmodifications will be I claim: Y

l. Apparatus for feeding ash at a controlled vrate com- 70 ,Y A Y Y Y'prlslngz Yan ash receiving hopper; an ash outfeed mechapr'ising: apluralityof ash `receiving hoppers; a vacuum being one such mechanism incommunication between `be closed if the Vhopper 1 is Vempty and thehopper 2 is V3. Apparatus for feeding Vash at af controlled rate,comprising: a -vacuum conveyor conduit; vacuum means for drawing airthrough'said conduit to move a predeter- I mined volume of ash per unittime; dust,collector means to receive ashmoved through said conduit; apluralityV of ashreceiving hoppers; a separate aerating chamberin directcommunicationvwith each of said hoppers,V each f said aerating `chamberhaving an outlet orifice' in communication with said conduit, the areaofA a singleoriiice being so Vsmall in proportion to the total area ofal1 said oricesthat the reduction of vacuum Vin said conduit resultingfrom free flow of airthrough a'hopper produces only a small reductioninthe ash moving characteristics of the apparatus;,means foraeratingrthe ashV in all said aeratingV chambers; and control meansrtolimit the operation of said aerating means in accordance with the levelof vacuum in the conduit.V I

4. AApparatus for feeding ash'at acontrolledrate, comprising: a vacuumconveyor conduit; vacuum means for drawing air through said conduit tomove a predetermined Y Y volume of ash per unit time;V dust collectormeans to receive ash moved through said conduit; a plurality of ashreceiving hoppers; a separate aerating chamber in direct communicationwith each of said hoppers, each Ysaid aerating chamber having an outletorifice in communication with said conduit, the area'of a single oriicebeings'o small in proportion to the .total area of all said orifices Ythat' the, reduction of vacuum in said conduit resulting each of saidhoppersjand said vacuum system, eachoutfrom exhaustion ofthe ash fromany oneihop'per produces only a small reduction in the-ash movingcharacteristics of the apparatus; means-forV aerating the ash inallrsaid aerating chambers; a valve controlling ,the flow of air to'said aerating meanvsfand vacuum'operated control means 'for said valvein'communication with said Vacuum conveyor system to open and close saidvalve when the conduit is under vacuum, lsaid control meansbeing'constructed' andgarranged to stop the ilow of aerating air 'whenthe pressure in the system reaches a predetermined vmaximum, andtorresume the flow of said. aerating air Vwhen said-pessurereaches apredetermined intermediate level.Y Y 1' Y' 5. uApparatus for feedingyash at aV controlled rate, comnism connected with the bottom of saidhopper, said outtrolling the ow of air to said aerating means, saidvalve being of a type which has only a fully open and a fully closedposition; a vacuum conveyor system to transport ash discharged throughsaid feed opening, said system including a dust collector and means fordischarging ash from said collector to a storage bin; means forproducing a negative pressure in said vacuum `ssytem; starting means forfully opening said valve when the negative pressure in the systemreaches a predetermined minimum; and control means which responds tovariations in the negative pressure in said vacuum system to fully openand fully close said valve while the conveyor system is under vacuum,said control means being constructed and arranged to fully close saidvalve when the negative pressure in the system reaches a predeterminedmaximum, and to fully reopen said valve when said pressure reaches apredetermined intermediate level between said minimum and maximumpressures.

6. Apparatus for feeding ash at a controlled rate, comprising: an ashreceiving hopper; a pneumatic conveyor conduit; air moving means forproducing in said conduit an air pressure different from atmosphericpressure; flow control means positioned between said 'hopper and saidconduit to control the ow of ash from the hopper to the conduit, saidflow control means including a chamber having a feed opening ofrestricted size in a side wall, said chamber being providing withaerating means to iluidize material for free ow through the opening,iand a movable valve for selectively closing said opening, and said flowcontrol means varying rapidly between a first condition permitting no owof ash and a second condition permitting maximum ilow of ash throughsaid opening; and control means which responds to the pressure in theconveyor conduit to control said ow control means by varying it betweensaid rst and second conditions, said control means being constructed andarranged to place said flow control means in said second condition whenpressure in the conduit reaches a rst level close to atmosphericpressure at which flow of ash into the conduit is desired, to returnsaid ilow control means to said first condition when excessive ash inthe conduit causes pressure to reach a second level a maximum distancefrom atmospheric pressure, and thereafter to restore said flow controlmeans to said second condition when reduction of the quantity of ash inthe conduit has caused pressure in the conduit to reach a predeterminedintermediate level between said rst and second pressures.

7. Apparatus for feeding ash at a controlled rate, comprising: an ashreceiving hopper; a pneumatic conveyor conduit; air moving means forproducing in said conduit an air pressure different from atmosphericpressure; flow control means positioned between said hopper and saidconduit to control the flow of ash from the hopper to the conduit, saidflow control means including a chamber having a feed opening ofrestricted size in a side wall, said chamber being provided withaerating means to fluidize material for free flow through the opening,and said flow control means varying rapidly between a rst conditionpermitting no ow of ash and a second condition permitting maximum flowof ash; an air valve which closes to place said flow control means ins'aid first condition and which opens to place said means in said secondcondition; and control means which responds to the pressure in theconveyor conduit to open and close said air valve, said control meansbeing constructed and arranged to completely open said air valve whenpressure in the conduit reaches a rst level close to atmosphericpressure at which flow of ash into the conduit is desired, to completelyclose said valve when excessive ash in the conduit causes pressure toreach a second level a maximum distance from atmospheric pressure, andthereafter to again completely open said valve when reduction of thequantity of ash in the conduit has caused pressure in the conduit todrop to a predetermined level between said rst and second pressures.

8. Apparatus for feeding ash at a controlled rate, comprising: an ashreceiving hopper; a pneumatic conveyor conduit; air moving means forproducing in said conduit an air pressure dilferent from atmosphericpressure; flow control means positioned between said hopper and saidconduit to control the flow of ash from the hopper to the conduit, saidyflow control means including a chamber having a feed opening ofrestricted size in a side wall, said chamber being provided withaerating means to fluidize material for free flow through the opening,and said flow control means varying rapidly between a rst conditionpermitting no flow of ash and a second condition permitting maximum flowof ash; starting means for placing said i'low control means in saidsecond condition when pressure in the conduit reaches a rst level closeto atmospheric; and control means constructed and arranged to place saidlow control means in said first condition when excessive ash in theconduit causes pressure to reach a second Ilevel a maximum distance fromatmospheric pressure, and thereafter to restore said ow control means tosaid second condition when reduction of the quantity of ash in theconduit has caused pressure in the conduit to reach a predeterminedintermediate level between said rst and second pressures.

9. Apparatus for feeding ash at a controlled rate, cornprising: an ashreceiving hopper; a vacuum conveyor conduit; air moving means forproducing a negative pressure in said conduit; flow control meanspositioned between said hopper and said conduit to control the flow ofash from the hopper to the conduit, said flow control means including achamber having a feed opening of restricted size in a side wall, saidchamber being provided with aerating means to iluidize material for freeflow through the opening, and said -ow control means varying rapidlybetween a lirst condition permitting no flow of ash and a secondcondition permitting maximum flow of ash; an yair valve which closes toplace said flow control means in said first condition and which opens toplace said means in said second condition; starting means for openingsaid air valve when the negative pressure in the conduit reaches apredetermined minimum; and control means which responds to variations inthe negative pressure in the conduit to open and close said valve whilethe conduit is under vacuum, said control means being constructed andarranged to close said valve when the negative pressure in the conduitreaches a predetermined maximum, and to reopen said valve when saidpressure reaches a predetermined intermediate level between said minimumand maximum pressures.

References Cited in the le of this patent UNITED STATES PATENTS OetikerMar. 11, 1958

